consistent_min_safe_lsn.patch

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index d6fe205eb4..f57d67a900 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9498,7 +9498,7 @@ CreateRestartPoint(int flags)
  * * WALAVAIL_INVALID_LSN means the slot hasn't been set to reserve WAL.
  */
 WALAvailability
-GetWALAvailability(XLogRecPtr targetLSN)
+GetWALAvailability(XLogRecPtr targetLSN, XLogSegNo last_removed_seg)
 {
 	XLogRecPtr	currpos;		/* current write LSN */
 	XLogSegNo	currSeg;		/* segid of currpos */
@@ -9524,7 +9524,7 @@ GetWALAvailability(XLogRecPtr targetLSN)
 	 * the first WAL segment file since startup, which causes the status being
 	 * wrong under certain abnormal conditions but that doesn't actually harm.
 	 */
-	oldestSeg = XLogGetLastRemovedSegno() + 1;
+	oldestSeg = last_removed_seg + 1;
 
 	/* calculate oldest segment by max_wal_size and wal_keep_segments */
 	XLByteToSeg(currpos, currSeg, wal_segment_size);
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 1b929a603e..bd2e3e84ed 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -243,6 +243,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	MemoryContext per_query_ctx;
 	MemoryContext oldcontext;
 	int			slotno;
+	XLogSegNo	last_removed_seg;
 
 	/* check to see if caller supports us returning a tuplestore */
 	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
@@ -272,6 +273,14 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	rsinfo->setResult = tupstore;
 	rsinfo->setDesc = tupdesc;
 
+	/*
+	 * Remember the last removed segment at this point for the consistency in
+	 * this table. Since there's no interlock between slot data and
+	 * checkpointer, the segment can be removed in-between, but that doesn't
+	 * make any practical difference.
+	 */
+	last_removed_seg = XLogGetLastRemovedSegno();
+
 	MemoryContextSwitchTo(oldcontext);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
@@ -282,7 +291,6 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 		Datum		values[PG_GET_REPLICATION_SLOTS_COLS];
 		bool		nulls[PG_GET_REPLICATION_SLOTS_COLS];
 		WALAvailability walstate;
-		XLogSegNo	last_removed_seg;
 		int			i;
 
 		if (!slot->in_use)
@@ -342,7 +350,8 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 		else
 			nulls[i++] = true;
 
-		walstate = GetWALAvailability(slot_contents.data.restart_lsn);
+		walstate = GetWALAvailability(slot_contents.data.restart_lsn,
+									  last_removed_seg);
 
 		switch (walstate)
 		{
@@ -368,7 +377,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 
 		if (max_slot_wal_keep_size_mb >= 0 &&
 			(walstate == WALAVAIL_NORMAL || walstate == WALAVAIL_RESERVED) &&
-			((last_removed_seg = XLogGetLastRemovedSegno()) != 0))
+			(last_removed_seg != 0))
 		{
 			XLogRecPtr	min_safe_lsn;
 
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index e917dfe92d..c05a18148d 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -326,7 +326,8 @@ extern void ShutdownXLOG(int code, Datum arg);
 extern void InitXLOGAccess(void);
 extern void CreateCheckPoint(int flags);
 extern bool CreateRestartPoint(int flags);
-extern WALAvailability GetWALAvailability(XLogRecPtr restart_lsn);
+extern WALAvailability GetWALAvailability(XLogRecPtr targetLSN,
+										  XLogSegNo last_removed_seg);
 extern XLogRecPtr CalculateMaxmumSafeLSN(void);
 extern void XLogPutNextOid(Oid nextOid);
 extern XLogRecPtr XLogRestorePoint(const char *rpName);